The present invention relates to a process for recovering valuable metals from mixed waste secondary batteries including Li ion/Nixe2x80x94H/Nixe2x80x94Cd secondary batteries.
Due to its merits, such as a high electrical energy density, a high working voltage, a long cyclic life and no memory effect, etc., the lithium ion battery has been recognized as a battery system with a high potential for development. Currently, in addition to being widely used in various 3C products, the lithium ion battery is expected to replace batteries of lead acid, Nixe2x80x94Cd and Nixe2x80x94H, etc. and becomes a power source for electric cars. However, Nixe2x80x94Cd and Nixe2x80x94H secondary batteries are still being used in certain applications, and thus they stilled can be found in the waste secondary batteries recycled. Therefore, there is a need to develop an efficient process for recovering valuable metals from mixed waste secondary batteries.
U.S. Pat. No. 6,514,311 discloses a process for recovering metals from waste lithium ion batteries, wherein the waste batteries are calcined and sieved to generate an ash containing metals and metal oxides. The invented process includes subjecting the ash to a dissolution etching treatment, and a filtration treatment, and separately using a membrane electrolysis method to separate out metal copper and cobalt, wherein the acid generated on the cathode side in the electrolysis process can be recovered through a diffusion dialysis treatment. After electrolysis, the solution rich in lithium ion, after precipitating the metal impurities by adjusting the pH value, can be added with a carbonate ion to form a lithium carbonate. The disclosure of this patent is incorporated herein by reference.
The present invention discloses a process for recovering valuable metals from waste secondary batteries comprising lithium ion batteries, Nixe2x80x94H batteries and Nixe2x80x94Cd batteries, wherein said waste secondary batteries are calcined and sieved to generate an ash containing metals and metal oxides. Said process comprises the following steps:
a) dissolving said ash with a 2N-6N sulfuric acid aqueous solution;
b) adding an alkali to the resulting solution from step a) so that cadmium (Cd) ions and rare earth metal ions contained in the solution precipitate;
c) performing a solid/liquid separation on the resulting mixture from step b);
d) extracting the resulting solution from the separation in step c) with a first organic extractant to form an aqueous layer containing nickel (Ni) ions and cobalt (Co) ions and an organic layer rich in Cd, iron (Fe) and zinc (Zn) ions;
e) extracting the aqueous layer from step d) with a second organic extractant to form an organic layer rich in Co ions and an aqueous layer rich in Ni ions;
f) counter extracting the organic layer rich in Co ions from step e) with a sulfuric acid aqueous solution to obtain an aqueous layer rich in Co ions;
g) using the aqueous layer rich in Ni ions formed in step e) as an electrolysis solution, and using a voltage of 1.5-4.0 volts to perform an electrolysis, thereby forming by reduction a Ni metal on a cathode in said electrolysis;
h) using the aqueous layer rich in Co ions formed in step f) as an electrolysis solution, and using a voltage of 1.5-4.0 volts to perform an electrolysis, thereby forming by reduction a Co metal on a cathode in said electrolysis;
i) adding a water soluble carbonate to a residue solution after the electrolysis in step g), thereby forming a precipitation of lithium carbonate.
Preferably, steps a) and b) together comprises the following steps:
a1) dissolving said ash with a 2N-6N sulfuric acid aqueous solution;
a2) performing a solid/liquid separation on the resulting mixture from step a1);
a3) dissolving the solid resulting from the separation in step a2) with a 4N-12N sulfuric acid aqueous solution;
b1) evaporating water from the resulting solution from the separation in step a2), so that a precipitate containing cadmium sulfate as a major portion thereof is formed therein;
b2) adding an alkali to the resulting solution from the dissolution in step a3), so that a precipitate containing a hydroxides of rare earth metal, Fe(OH)3 and Al(OH)3 as a major portion thereof is formed therein;
wherein the mixture formed in step b2) is subjected to the solid/liquid separation in step c).
Preferably, the precipitate formed in step b1) contains 85% cadmium sulfate by weight of the precipitate.
Preferably, aid alkali used in step b2) is sodium hydroxide and said sodium hydroxide added in step b2) is in an amount so that the solution has a pH value of about 6.
Preferably, the mixture formed in step b1) is subjected to a solid/liquid separation, and the resulting liquid is used as a portion of the 4N-12N sulfuric acid aqueous solution used in step a3).
Preferably, said water soluble carbonate in step i) is sodium carbonate.
Preferably, the process of the present invention further comprises counter extracting the organic layer rich in Cd, Fe and Zn ions with a sulfuric acid aqueous solution to obtain an aqueous layer rich in Cd, Fe and Zn ions; and removing said Cd, Fe and Zn ions from said aqueous layer rich in Cd, Fe and Zn ions by using an ion exchange resin.
Preferably, the process according to the present invention further comprises smashing said calcined product, and collecting the smashed product passing through a screen of 20-5 mesh during smashing. More preferably, the process according to the present invention further comprises separating said smashed product with a screen of 10-5 mesh, thereby obtaining an under size portion containing the ash containing metals and metal oxides, and a portion remained on the screen.
Preferably, the process according to the present invention further comprises separating iron from the portion remained on the screen by a magnetic selection process. More preferably, the process according to the present invention further comprises separating copper and aluminum from the residue generated after the magnetic selection by an eddy current selection process.
The process of the present invention provide a comprehensive recovery of valuable metals from the mixed wasted Li ion/Nixe2x80x94H/Cdxe2x80x94Ni secondary batteries by incorporating an effective physical selection method and a chemical purification system adapted to the metals contained in the mixed waste secondary batteries, whereby the recovery and purity of the metals recovered are enhanced.